The present invention relates to a vehicle driveline clutch and, more particularly, to a vehicle driveline clutch where a friction disc is clamped to an engine flywheel using an electronically controlled one-way clutch and used to provide a drive and coast driveline clutch lock-up and release.
Driveline clutches commonly use a plurality of high rate coil springs to clamp a pressure plate against a friction disc to an engine flywheel. The springs are disposed within a pressure plate assembly which is bolted to the engine flywheel. A mechanical linkage controls the pressure plates spring mechanism is displaced through action of the operator to control the lock-up and release of the driveline clutch.
There have been extensive efforts to automate the operation of the driveline clutch using electronics to allow for its operation independent of actions of the operator. It is known to use an electro-mechanical or hydraulic powered actuator connected to a mechanical linkage to, in essence, replace the operator for more accurate clutch operation during transmission shift events. Using such an actuator, the mechanical linkage is moved in response to an electrical control signal generated by a microprocessor-based control unit which is used to process a variety of vehicle sensor inputs and other operating conditions to determine when and in what manner the driveline clutch should be activated or deactivated.
The use of a ball ramp actuator to load a clutch pack in a vehicle driveline is known. U.S. Pat. No. 4,805,486 discloses a limited slip differential where a clutch pack is loaded in response to the activation of a ball ramp actuator initiated by rotation of a servo motor or a solenoid driven brake shoe acting on an activating ring. A ball ramp actuator has also been utilized in a vehicle transmission to engage and disengage gearsets by loading a gear clutch pack in response to a signal as disclosed in U.S. Pat. No. 5,078,249, the disclosure of which is hereby incorporated by reference.
U.S. Pat. No. 5,469,948 and U.S. Pat. No. 5,485,904, the disclosures of which are hereby incorporated by reference, disclose clutch ball ramp actuators which utilize a coil to energize and provide a breaking force to a control ring thereby activating a ball ramp actuator to supply a clamping load on a friction disc. Both of these patents also disclose the use of a one-way clutch to prevent rotation of the control ring in a direction releasing the driveline clutch where one side of the one-way clutch is connected to the output shaft (transmission input shaft) using the control coil such that the one-way clutch is only active when the control coil is energized.
The advantage of the ball ramp mechanism as compared to other actuators is that it converts rotary motion into axial motion with a very high force amplification, often 100:1 or greater. In most of these applications, one side of the ball ramp actuator, commonly called a control ring or plate, reacts against case ground through the force induced by an electromagnetic field generated by an electrical current in a coil or, in the alternating, the control ring is rotated by an electric motor relative to case ground. To generate greater clamping forces, electrical current supplied to the coil motor is increased thereby increasing the reaction of the control ring case ground which rotates the control ring relative to an activation ring thereby causing rolling elements within the ball ramp mechanism to engage corresponding ramps in the control and activation rings which increase the axial movement and clamping force on the clutch disc. One problem with the use of the ball ramp actuator to supply the clutch clamping force is that the mechanics of a single ramp ball ramp mechanism results in a loss of clamping force when the energizing current is removed.
In otherwords, this type of a prior art ball ramp actuated clutch will cause the driveline clutch to disengage when the clutch control unit fails to supply electrical energy into the coil. The ball ramp actuator is then free to move in a direction that results in deactivation of the driveline clutch. In this circumstance, the relative rotation of the activation ring and control ring has been reversed such that the ball ramp axial displacement is collapsed thereby allowing the pressure plate to pull away from the clutch disc. The result is that the engine is disengaged from the transmission and any engine drive or braking effect is eliminated. It would be desirable for the ball ramp actuator to maintain its state (position) upon the loss of power from the clutch control unit.
The ball ramp actuator comprises a plurality of rolling elements, control ring and an opposed activation ring where the activation ring and the control ring define at least three opposed single ramp surfaces formed as a circumferential semi-circular grooves, each pair of opposed grooves containing one roller element. A thrust bearing is interposed between the control ring and a housing member, rotating with and connected to the input member such as a flywheel. An electromagnetic coil is disposed adjacent to one element of the control ring so as to induce a magnetic field that loads the control ring which in turn causes relative rotation between the control and activation rings of the ball ramp actuator.